1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine, particularly a control apparatus including a disconnection failure detection function for a fuel injector.
2. Description of the Background Art
Fuel injection at an internal combustion engine is generally executed by an injector (fuel injection valve) provided at each cylinder. An injector is formed including a solenoid coil acting as an electromagnet when current is applied in response to a fuel injection signal. The period of fuel injection from the injector must be set precisely in order to achieve an appropriate fuel injection timing and fuel injecting quantity corresponding to the operating state of the internal combustion engine.
An injector of a general configuration has the fuel injection period controlled by regulating the current applied to the solenoid coil that functions as an electromagnet when current is applied. Specifically, when current is not applied to the solenoid coil, the injection hole of the injector is blocked by a needle that is pushed from behind in response to the force of the spring arranged at the rear side of the plunger core. When current is applied the solenoid coil, the plunger core is attracted by the generated magnetic force. This movement of the plunger core causes the needle to be removed from the injection hole, whereby fuel is injected at a predetermined pressure from the injection hole.
In the case where current is not applied to the solenoid coil when a fuel injection signal is generated due to occurrence of disconnection failure at the injector, fuel injection cannot be conducted in a desirable manner. This may cause engine output degradation, leading to the possibility of adversely affecting the operation status of the vehicle. Therefore, disconnection failure at an injector must be promptly identified, including which injector has failed, and inform the driver of the failure.
In view of the foregoing, there is proposed a system of detecting and identifying disconnection at each signal line through which a fuel injection signal is transmitted for each cylinder in an internal combustion engine with a plurality of cylinders (for example, Japanese Patent Laying-Open No. 2004-137938; hereinafter referred to as Patent Document 1). The disconnection detection apparatus for an internal combustion engine disclosed in Patent Document 1 has a history flag generated, representing whether each of fuel injection signals received in parallel for each cylinder from the main control circuit had been received or not. By monitoring the status of the history flag stored in a memory, the cylinder with disconnection at the signal line can be identified.
As one type of engine, there is known an internal combustion engine that includes an in-cylinder injector directly injecting fuel into the combustion engine and an intake manifold injector injecting fuel into an intake port (intake manifold) for each cylinder. For such an internal combustion engine, there is proposed a configuration in which the in-cylinder injector and intake manifold injector are used appropriately so as to partake in fuel injection in an even combustion operation mode of (for example, Japanese Patent Laying-Open No. 2002-364409; hereinafter referred to as Patent Document 2).
In an internal combustion engine of a configuration that includes both an in-cylinder injector and an intake manifold injector, as disclosed in Patent Document 2, there will be an appreciable number of injectors arranged for the entire internal combustion engine. In the case where the internal combustion engine takes a configuration in which a mechanism is provided corresponding to each injector, the number of failure detection mechanisms that has to be arranged will also be appreciable. It is therefore necessary to arrange efficiently a failure detection configuration that allows identification of the injector where disconnection failure has occurred.